Android studio why can't I run the project on my mobile phone?

I connected my Samsung galaxy S7 to my laptop with a USB, but why isn't it there?

As it says in the message: You are using an SDK version that is newer than the version supported by the device. You have to use an older SDK version, otherwise features may be used that are not yet available on the device.

How can i use an older version?

Unfortunately I do not know it.

… The www says: https://www.geeksforgeeks.org/how-to-change-the-api-sdk-level-in-android-studio/

Have looked, now know how to change it, but which version do I have to change it to?

In the middle is a list with which you can read the API level based on the Android version:

https://docs.microsoft.com/...bs=windows

The app is now on my mobile phone, but when I want to go in it says "My application keeps stopping", even though I have the correct version

Unfortunately, I can't help you with that.

Ok anyway thanks have brought me further than I was before